DE 10 2008 015 412 has disclosed a vibration damper of this type. Said vibration damper comprises a damper tube which is filled with damping liquid, a piston rod which can be retracted and extended in the damper tube, a working piston which is attached to the piston rod and divides the interior space of the damper tube into a piston rod-side working space and a working space which is remote from the piston rod, and a first and a second damping valve in each case with a separately adjustable damping force. The first damping valve is passed through by the damping liquid in the case of a retraction movement, and the second damping valve is passed through by the damping liquid in the case of an extension movement of the piston rod. The damping force of the two damping valves is set by way of in each case one separate electrically controllable drive device. Each damping valve comprises a valve body which can be moved in a defined manner between a closed position and an open position using the drive device. The valve bodies are loaded into a closed position in each case by way of a restoring means.
In a currentless state, the valve body of the two damping valves is situated in a closed position on account of the loading by way of the restoring means; as a consequence, the damping valves are what are known as “normally closed” valves (NC valves). Although satisfactory emergency running properties (failsafe behavior) can in principle be set by way of valves of this type, NC valves of this type have a high energy consumption since energy has to be consumed continuously, in order to achieve at least partial opening of the valve.
Although what are known as “normally open” valves (NO valves) might be used instead of the NC valves, NO valves of this type are loaded into their open position by way of restoring means and therefore require less energy during normal operation than NC valves. Said NO valves are not suitable for setting emergency running properties, however, since, in the currentless state, the damping liquid can flow through the valve in a largely unimpeded manner, and a soft characteristic is therefore produced.
As a consequence, it is an object of the present invention Thus a need exists to reduce the energy consumption of a vibration damper of the generic type, but at the same time to ensure that the vibration damper has sufficient emergency running properties.